Hello! Welcome and thank you for asking on HCM! I understand your concern and would explain that his symptoms may be related to seizures or hypoxia. The latest episode with shivering and blue nails may be related to hypoxia or a seizure. Does he have any other symptoms besides headaches? I would recommend consulting with the GP for a careful physical examination, a resting ECG, a chest x ray study and some blood lab tests: -complete blood count -PCR, sedimentation rate (inflammation) -blood gass analysis -blood electrolytes -fasting glucose -kidney and liver function tests. A brain EEG may be needed to exclude possible seizures, followed by a brain CT scan (to exclude a possible brain lesion). Hope to have been helpful! Best wishes, Dr. Aida